The invention relates to a pallet container having a thin-walled rigid inner receptacle made from thermoplastic material for the storage and transport of fluid or free-flowing goods, wherein the plastic container is closely surrounded by an outer cage jacket as a supporting casing of crossed hollow bars and a bottom pallet on which the thermoplastic receptacle is supported and which is firmly connected with the supporting casing.
Pallet containers of the type that have a supporting casing from welded hollow bars are generally known, as for example the pallet container disclosed in EP 0 734 987 A (Sch). The supporting casing of the pallet container disclosed there consists of hollow bars having a circular profile that are highly compressed at the welded intersection points. From EP 07 55 863 (F) another pallet container is known with hollow bars that have a square profiled cross section and that are each partially slightly compressed, about 1 mm, at four contact points and only in the areas of intersections in order to facilitate a better welding action, while along the entire length of the hollow bars, they retain a cross section without any dimples, or have any cross section-reducing dents whatsoever.
Another pallet container, known from the DE 196 42 242 A, has a cage jacket from hollow bars that have an open trapezoid shaped profile, where the straight surfaces laterally flanged outwards, are welded together in the area where the bars intersect.
The bottom pallet of the pallet containers may be configured as a flat pallet made from plastic or wood or configured as a steel tube frame; and attachment of the cage jacket is usually realized by attachment means such as for example, screws, brackets, clamps or grips that engage with the lower horizontal and circumferentially extending cage bars. These attachment means are nailed, riveted, screwed or welded to the upper plate or the upper outer edge of the pallet.
The drawbacks of the embodiment of a pallet container disclosed in the afore-described EP 0 734 967 A are such, that the circular hollow profile of the horizontal and vertical cage hollow bars, particularly in the area of the intersections, are prone to considerable deformation, specifically at the side of the welding points and therefore exhibit a markedly reduced section modulus as compared to the other areas. Also, welding the hollow bars causes material brittleness precisely in the area of the dented hollow bar profile. Additionally, the hollow bar profile is still deeper dimpled next to the dimples for the welding points and thus, further weakened.
In industrial applications, for example when the pallet containers are utilized in the chemical industry, they have to pass a governmental approval inspection and fulfill various quality controls. For example, the filled pallet containers have to undergo interior pressure tests and drop tests in which the pallet container is dropped from specified heights. Pallet containers or combination IBCs (IBC=Intermediate Bulk Container) of the type discussed here—with a filling volume of usually 1000 liters—are preferably used in the transport of liquids. When transporting filled combination-IBCs in particular by truck, the content in the fluid container is prone to considerable gushing motions which are generated by transport shocks, such as for example when the transport vehicle rides on bumpy roads. Thus, constantly changing pressure forces are exerted on the interior receptacle walls, which in turn lead to radial vibrational motion of the cage jacket (dynamic continuous vibrational stress). Depending on the configuration of the cage jacket, especially during long transports over bad roads, vibrational stress builds up to such an extent that the cage bars get fatigued and/or break. Pallet containers of this type are therefore not suitable for multiple usage or for export to the USA.